In general, until to finish one semiconductor product from a wafer, a series of very complex semiconductor processes are required. A variety of semiconductor processing equipments each are used in a series of semiconductor processes. Operation performance (that is, process conditions) of the semiconductor processing equipments each is a factor of determining operation performance of finished semiconductor products. Accordingly, abnormal process errors of the semiconductor processing equipments become major obstacles to obtain a good quality of semiconductor product as well as cause economic loss and time loss.
One of the semiconductor processing equipments is a plasma reactor. The main use of the plasma reactor is to etch a wafer surface according to a specific pattern or deposit deposition materials on a wafer top surface according to a specific pattern. The plasma reactor includes a plasma reaction chamber and a plasma reaction controller. During an etch or deposition process, a target wafer is mounted within the plasma reaction chamber and plasma reaction conditions such as a pressure, a reaction gas, and power within the plasma reaction chamber are controlled by the plasma reaction controller. For the plasma reaction controller to accurately control the plasma reaction conditions is of much importance, for example, to prevention of process errors such as over-etch during a plasma etch process. The plasma reaction controller has to accurately detect an in-chamber status in order for the plasma reaction controller to accurately control the plasma reaction conditions within the plasma reaction chamber. For this, a conventional plasma reactor for detecting an etch endpoint using a monochromator has been developed.
The conventional plasma reactor includes a reaction chamber, an optical fiber cable, the monochromator, and an endpoint detection device.
The optical fiber cable collects a single wavelength light emitted from the inside of the reaction chamber through a window provided in an outer sidewall of the reaction chamber and forwards the collected lights to the monochromator. The single wavelength light can be lights generated when a component (e.g., etched material) serving as a criterion for determining an etch endpoint of a target wafer reacts with plasma.
The monochromator converts the single wavelength light received from the optical fiber cable into a voltage level signal and outputs the voltage level signal to the endpoint detection device.
The endpoint detection device detects an etch endpoint on the basis of the voltage level signal received from the monochromator. For example, the progress of an etch process brings about a reduction of etched material and resultantly, a reduction of even lights generated by the etched material. In conclusion, the endpoint detection device determines that an etch endpoint is a time point of reduction of light generated by the etched material, using the voltage level signal received from the monochromator.
As described above, the conventional plasma reactor detects an etch endpoint using the single wavelength light. However, a wavelength of lights generated by etched materials is distributed over several frequency bands and therefore, it is very difficult to select one wavelength of most significance serving as a criterion for determining an etch endpoint. Also, as a percentage of total area to open area of a target wafer is extremely less, a noise of the single wavelength light increases. This is shown in detail in FIGS. 1A to 1C.
FIG. 1A shows a time-dependent variation of a prediction value for determining an etch endpoint when an open area rate is equal to 3%. Like FIG. 1A, FIGS. 1B and 1C each show time-dependent variations of prediction values for determining etch endpoints when open area rates are equal to 0.7% and 0.5%. In FIG. 1A, a waveform shows a clear etch endpoint (E) because of a large difference between prediction values before and after the etch endpoint (E). However, in FIGS. 1B and 1C, a waveform shows an unclear etch endpoint (E) because of a very small difference between prediction values before and after the etch endpoint (E). As described above, in a method for detecting an etch endpoint using a single wavelength, when the percentage of total area to open area is a few percents or less, the etch endpoint is not actually detected with accuracy.
For a solution to disadvantages of the etch endpoint detection method using the single wavelength, a research on a method for detecting an endpoint using a whole wavelength has been conducted a lot. To realize this, Principal Component Analysis (PCA), a kind of multivariate statistic analysis method, has been used. PCA (Jackson, 1981) is a method of representing a number of variate values by one or a few synthetic indicators (main components) with no information loss as possible. PCA includes converting lights of several wavelengths, which are emitted from the inside of a chamber with execution of an etch process, into voltage level data, normalizing the voltage level data, processing the normalized data by PCA, computing part of result values obtained by PCA processing and the normalized data, and detecting an etch endpoint on the basis of the result values of the computing. However, in a conventional endpoint detection method using PCA, a detection speed is very slow because it actually takes a long time to real-time normalize voltage level signals (that is, Optical Emission Spectrometer (OES) data). In conclusion, PCA is almost impossible to real-time determine an in-chamber status quickly and thereby the plasma reaction controller is impossible to real-time control reaction conditions within a plasma reaction chamber as well. This problem becomes more serious because of the recent development of sensors to have as better operation performance as the sensors receive light signals of thousands of wavelengths at several times even for one second. That is, the sensors can receive a large amount of light signals with the improvement of operation performance of the sensors; however, it takes a very long time to store and normalize voltage level data corresponding to the large amount of received light signals. Accordingly, an endpoint detection speed gets slower and resultantly, it is impossible to control plasma reaction conditions in real time.